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Soil test to get the best

Warm weather makes farmers think about planting, and soil testing can ensure plants get what they need to thrive.

Crops, whether they’re fruit, field crops or garden
vegetables, require proper nutrition for best results. Knowing what nutrients
are needed, and how much, is a key to success. Soil testing provides a window
into the soil’s nutrient status and the results address the plant’s needs. Testing
also helps us manage our fertilizer dollars wisely and protect the environment
from over application of nutrients. Nitrogen applied in excess of the plant’s
needs can leach with rain, down to the groundwater. Over-application of
phosphorus can lead to runoff or wind erosion moving it to surface water. Since
phosphorus is commonly the limiting nutrient in our lakes and streams, this phosphorus
addition can cause stimulation of unwanted algae and other aquatic plants, resulting
in fish die-offs and loss of quality recreational waters.

Plants require at least 16 elements for growth. Carbon,
hydrogen and oxygen come from air and water and make up over 90% of the fresh
weight of plants. The rest of the plant’s weight is made up of the needed
macronutrients (nitrogen, phosphorus, potassium, sulfur, calcium, and
magnesium) and micronutrients (zinc, copper, iron, manganese, boron, chlorine,
molybdenum, and cobalt), which plants get from soil, compost or fertilizer. The
macronutrients are needed in greater quantities while only very small amounts
of the micronutrients are required. The chlorine requirement for example, was
unrecognized for years, because the amount needed was so minute that enough was
residual on the well-washed research glassware.

Nutrient recommendations have changed over the years. The
changes are based on changes in crop varieties and research results in controlled
field studies. For example, some new corn varieties provide high yields with
less nitrogen than older varieties. However, it is still recommended for long-term
nutrient management, that producers sample a field at the same time of year
each time the field is sampled, and that fields be sampled regularly. For
vegetables, sample at least every two years. For field crops, sample every three
years. Sampling depth depends on the plow depth and type of crop.

In addition to nutrients, a soil test provides the pH. This
indicates how acid or alkaline the soil is; pH affects nutrient availability. For
example, plants growing in a high pH (alkaline) soil containing iron will be
iron deficient because the iron is bound and unavailable to the plants. For
good plant growth, the pH of this soil will need to be lowered.

Producers can take their own soil samples or hire someone to
do it. If a field is uniform and has a uniform cropping history for the past
two years, 20 samples can be taken from up to 40 acres, mixed up for a
composite sample from which a representative subsample is submitted for testing.
However, if there is variation in cropping history, soil type, slope, tillage
practices, manure/fertilizer management, etc. the field needs to be subdivided
and sampled based on site similarity and fertilizer application plans. Representative
sampling provides meaningful information for fertilizer management. Soil testing
can be obtained through the MSU
Soil and Plant Nutrient Laboratory as well as some commercial laboratories.

Nitrogen, potash and phosphate fertilizer prices are up from
last year. If the weather gradually warms across the United States, supply will
match fertilizer demand as producers begin the planting season from south to
north, and fertilizer prices will remain stable. If, however, the Corn
Belt and the northern areas all have fertilizer demand at the same time,
there could be an additional increase in prices. This would further boost the
importance of soil testing to maximize fertilizer dollars.

November 21, 2017 | Erin Lizotte | As the end of the year approaches, growers can take advantage of the new online Integrated Pest Management Academy and earn six credits towards their Michigan Pesticide Applicators License.